1. Field of the Invention
This invention relates to a liquid crystal display, and more particularly to a light unit in the liquid crystal display that has a high focusing ability.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) controls a transmitted amount of light beams supplied from a back light unit by means of a liquid crystal panel consisting of a number of liquid crystal cells arranged in a matrix type and a number of control switches for switching video signals to be applied to the liquid crystal cells, thereby displaying a desired picture on a screen. The back light unit will be described with reference to FIG. 1 and FIG. 2 below.
Referring to FIG. 1, the conventional back light unit includes a light-guide plate 4 for guiding light beams passing through a light input 20, a reflective plate 2 arranged under the light-guide plate 4 to reflect light beams progressing toward the lower surface and the side surface of the light-guide plate 4 into the upper surface thereof, a first diffusion sheet 6 for diffusing light beams passing through the light-guide plate 4, first and second prism sheets 8 and 10 for controlling a progress direction of light beams passing through the first diffusion sheet 6, and a second diffusion sheet 12 for diffusing light beams passing through the prism sheets 8 and 10. The light input 20 consists of a lamp 22 for generating light beams, and a lamp housing 24 for packaging the lamp 22 and reflecting the light beams from the lamp 22 into the light-guide plate 4. The lower surface of the light-guide plate 4 is provided with a printed pattern. This printed pattern does not meet a total reflection condition of the light beams passing through the light input 20, thereby allowing the light beams to be uniformly progressed into the upper surface of the light-guide plate 4. At this time, the light beams progressing toward the lower surface and the side surface of the light-guide plate 4 are reflected by the reflective plate 2 to be progressed into the upper surface thereof. The light beams passing through the light-guide plate 4 are diffused into the entire area by means of the first diffusion sheet 6. The light beams incident to a liquid crystal panel (not shown) have a large light efficiency at right angles. To this end, it is desirable that two forward prism sheets are disposed to make a progress angle of the light beams outputted from the light-guide plate 4 perpendicular to the liquid crystal panel. As shown in FIG. 1, the light beams passing through the first and second prism sheets 8 and 10 are incident to the liquid crystal panel via the second diffusion sheet 12. The conventional back light unit having the configuration as described above cannot obtain a desired view angle profile until two prism sheets are included. Accordingly, it has problems in that light loss does not only increase, but also a manufacturing costs rise. A structure that has been suggested for the purpose of solving the above-mentioned problems is shown in FIG. 2.
Referring now to FIG. 2, the conventional back light unit includes a light-guide plate 4xe2x80x2 for guiding light beams passing through a light input 20, a reflective plate 2 arranged under the light-guide plate 4xe2x80x2 to reflect light beams progressing toward the lower surface and the side surface of the light-guide plate 4xe2x80x2 into the upper surface thereof, a prism sheet 14 for controlling a progress direction of the light beams passing through the light-guide plate 4xe2x80x2, and a diffusion sheet 12 for diffusing light beams passing through the prism sheet 14. Since the light input 20 and the reflective plate 2 have the same function and operation as those in FIG. 1, an explanation as to them will be omitted. The lower surface of the light-guide plate 4xe2x80x2 is provided with a prism-shaped pattern. This prism-shaped pattern does not meet a total reflection condition of the light beams passing through the light input 20, thereby allowing the light beams to be uniformly progressed into the upper surface of the light-guide plate 4xe2x80x2. A backward prism sheet 14 is arranged over the light-guide plate 4xe2x80x2. In this case, it is desirable that, since an angle of the light beams outputted from the light-guide plate 4xe2x80x2 is more than about 65xc2x0, vertical angles of the prism sheet 14 should maintain 63xc2x0 to 70xc2x0. Thus, the light beams passing through the prism sheet 14 make right angles with respect to the liquid crystal panel. The light beams passing through the prism sheet 14 are diffused into the entire area by means of the diffusion sheet 12. The conventional back light unit having the configuration as described above has problems in that, since the backward prism sheet 14 is included, the wall surface of the light-guide plate 4xe2x80x2 not only get reflected, but also bright lines of the light input 20 are seen. Therefore, it is necessary to provide a back light unit with a high focusing ability that is capable of reducing the manufacturing cost as well as minimizing the wall surface reflection and the bright lines of the light input.
Accordingly, it is an object of the present invention to provide a light unit in a liquid crystal display that has a high focusing ability.
In order to achieve these and other objects of the invention, a light unit in a liquid crystal display according to the present invention includes a light input for directing a light path of a light beam to the rear side thereof to obtain high focusing of the light beam. The present light unit further includes a light guide for allowing the light beam from the light input to progress in the vertical direction of a liquid crystal panel.